Gaseous reduction of oxygencontaining copper



June 20, 1961 c. R. KUZELL ETAL 2,989,397

GASEOUS REDUCTION OF OXYGEN-CONTAINING COPPER Filed July 15, 1959 whit vllllll ll it d S ates. Pat f 2,989,397 GASEOUS REDUCTION OF OXYGEN- CONTAINING COPPER Charles R. Kuzell, Phoenix, Morris G. Fowler, Douglas, Leonard Klein, Scottsdale, and John H. Davis, Jr.,

Douglas, Ariz., assignors to Phelps Dodge Corporation, New Yorl r, N ,Y., a corporation of New York Filed July 15, 1959, Ser. No. 827,188 11 Claims. (Cl. 75-76) This invention relates generally to the pyrometallurgical refining of molten copper by the consecutive steps of oxidation and reduction. More particularly it relates to the reduction step wherein unwanted oxygen contained in oxygen-containing copper is removed from the copper by the use of a gaseous reductant. Still more specifically the invention relates to the successful and economical use of gaseous reductant in lieu of heretofore used tree trunks, commonly referred toas poles,

The use of poles or logs, commonly referred to in the copper refining art as poling, is well known. Poling is practiced to remove unwanted oxygen from the molten copper which contains this oxygen. In the poling of copper the pole of green timber is forced below the surface of the molten copper bath so as not only to erupt the liquid metal into a fountain in the reducing. atmosphere of the draft-dampered furnace but also to stir vigorously the whole bath by the rapid evaporation of moisture and volatile matter from the green wood. The duration of poling a large batch of copper is several hours for the reduction of theoxygen to the end-point which is usually less than 0.1 to 0.2% as desired. This procedure is, comparatively speaking, very expensive and is subject to many drawbacks. Nevertheless, the poling practice'has continued for considerably more than half a century and is still conventional practice despite many prior suggestions, in issued patents and in the literature, of methods for accomplishing the same ends as the poling operation, which purport to eliminate the use of poles and it has many times been suggested that other reducing agents, such as coal, charcoal, petroleum, natural gas or manufactured reducing gases of various kinds, be used in lieu of timber poles. Notwithstanding these many prior art suggestions, none of them, so far as we are aware, has ever achieved only metallurgical success or both metallurgical and economical success. None of the prior suggestions, so far as we are aware, has been practiced industrially. For one reason or another they have not been satisfactory and have not gone into use. So the use of poles still continues in the art despite the ever increasing scarcity and cost of suitable timber poles and despite the many drawbacks attributable to their use.

In accordance with our invention the use of timber poles or logs, with its attendant hazards and drawbacks, is eliminated and we are able to remove unwanted oxygen from molten oxygen-containing copper by the use of a gaseous reductant which has proved itself in actual large scale commercial operations not only to be successful and effective for the metallurgical purpose but also more economical and less hazardous to use than timber poles.

In accordance with our invention we use as thereductant a gaseous reducing agent which is obtained by a partial oxidation of low molecular weight hydrocarbons of the straight chain parafi'ln series (C H and preferably natural gas in which methane (CH.,,) is the predominant constituent, it being understood of course that there is normally present in natural gas, smaller amounts of hydrocarbon compounds of molecular weight higher than methane, such as ethane (C H propane (C H and often there is present compounds of still higher Patented June 2 0, 1961 molecular weight, such as butane (nor'mal C H and iso C H pentane (C H and not infrequently small amounts of nitrogen (N2), carbon dioxide (CO and even oxygen (0 and perhaps other gases or elements in very small amounts. And While we prefer toproduce our gaseous reducing agent from a natural gas in which methane is the predominating hydrocarbon compound, our invention contemplates as a starting material for producing a suitable gaseous reducing agent the use of hydrocarbon mixtures in which other hydrocarbon com pounds than methane predominate, such as hydrocarbon gases in which ethane, butane, propane, pentane or mixtures of these hydrocarbons predominate.

In practicing our preferred method, which we have now carried out in day-to-day operations on a large commercial scale with excellent results at a large copper smelting and refining plant we have used natural gas supplied by a natural gas public utility company and produced from New Mexico and Texas fields. While the natural gas supplied my vary somewhat from time to time, the following is a typical analysis of the natural gas.

Volumetric Content,

Component percent Methane-CH4 8 Oxygen-Oz The calculated molecular weight of that gas is 18.79 The calculated formula is eli zed alumina or other suitable catalyst, under condi tions which convert the major part of the combined carbon (C) present in the mixture of natural gas and air to carbon monoxide gas (CO) and the major part of the combined hydrogen (H) present in the natural gas to hydrogen (H Minor amounts of CO and H 0 will be formed and possibly some carbon (C) and there may be a minor amount of hydrocarbon, such as CH present which remains unreacted, and of course the nitrogen (including argon and other rare gases) in the air or in the natural gas itself, is inert and is present in the resultant gaseous mixture. ture of this partial oxidation of natural gas is referred to herein as reformed gas.

As an example of this resultant gaseous mixture or reformed-gas, there is shown below the analysis of this reformed gas as produced by us in a gas reformer and used in the practice of our process for removal of unwanted oxygen from molten copper, the copper having been subjected to the oxidizing step of fire-refining, in-

This resultant gaseous mix- 002, CO, H2, H10, CH4, N2, perperper perperpcrcent cent cent cent cent cent This reformed-gas was produced in a gas reformer apparatus in which nickelized alumina is used as the catalyst. The reformed-gas issuing from the reformer had a temperature between 1500 and 1800 F. at a low pressure of a few pounds. It was conducted through the cooling chamber of that apparatus where it was cooled to 100 F.l50 F. It was compressed and conducted through a reservoir or receiver and then through conduits to an anode furnace into which had been charged molten copper from a previous converter operation.

As is well known, air is blown through molten matte in the converter to remove iron, sulfur, and other unwanted components, which by their chemical aflinity to oxygen are burned out before the copper begins to oxidizc, at which point the air-blowing is terminated. The molten copper as drawn off from the converter is never suitable for commerce and it therefore has to go through an additional process called fire-refining, consisting of the aforementioned steps of oxidation, slag removal and reduction. Such fire-refining is essential when the copper is to be further refined by electrolysis to remove silver, gold and other impurities and it is also necessary to the attainment of the desired purity and physical properties even when electrolytic refining is unnecessary and it is desired to cast the copper directly into commercial wirebars, cakes, ingots, or billets, instead of anodes. The first step of a fire-refining process is that of oxidation and leaves so much unwanted oxygen in the copper that the reduction or oxygen-removing step is necessary. Our process removes this unwanted oxygen by the use of reformed natural gas as a reductant, in lieu of the use of timber poles, which had heretofore been used in the poling operation for the removal of the unwanted oxygen.

After the final air-blowing of the copper at which point the copper was ready for poling, the reformed gas was introduced through suitable gas lines and thence through tuyeres placed in the anode furnace, into the batch of molten copper under the surface of the copper in the furnace. This anode furnace was one in which poling had previously been practiced to produce toughpitch copper for casting into anodes to be subsequently refined in electrolytic cells; such copper being referred to as anode copper when it is used for casting into anodes. But for the gas lines and tuyeres, the furnace was conventional. The gas lines running to the tuyeres were, of course, equipped with the necessary valves to regulate the flow of the reformed-gas through the tuyeres and to shut off the fiow of gas when the proper amount of oxygen removal had been accomplished.

The control of operation of the anode furnace with the reformed-gas was virtually the same as with poling. That is, test buttons were taken regularly and examined for the determination of the state of progress of the reduction of the charge. The same criteria are used for either method of operation. As in the poling process small sample quantities are withdrawn from the molten copper bath from time to time as the process proceeds and these samples allowed to cool and solidify. As a plant control test the oxygen in the copper will have been reduced to the desired point, i.e. to the tough-pitch stage, when a sample button on cooling solidifies with the desirable surface characteristics such as a flat or slightly convex, wrinkled surface. When reduction (oxygen removal) has proceeded to such end point, casting of the finished charge into copper anodes suitable for electrolytic refining is carried out in the usual or conventional manner.

Although the novel features which are believed to be characteristic of our invention are pointed out in the annexed claims, the invention itself as to its objects and advantages and the manner in which it may be carried out, may be better understood by reference to the following more detailed description and examples, taken in connection with the accompanying drawings, forming a part hereof, in which FIG. 1 is a view, largely diagrammatic, of apparatus for carrying out our process, showing a gas reformer, gas cooler, receiver, and conventional anode furnace, modified by addition of tuyeres;

FIG. 2 is an end view of the furnace on line 2-2 of FIG. 1;

FIG. 3 is an end view of the furnace on line 33 of FIG. 1; and

FIG. 4 is a broken-away sectional view to larger scale showing a typical tuyere.

Referring now to the drawings in which like reference characters indicate like parts throughout the several views, there is illustrated, largely in diagrammatic fashion, one form of apparatus in which our process may be carried out. As shown, the apparatus, in general, comprises a natural gas reformer A, a suitable furnace B, in which to treat molten copper, and a suitable conduit system C to lead the reformed-gas from the reformer A to tuyeres D located in the furnace in a position to intro duce the gaseous reductant into the molten bath E of copper beneath its surface in such manner as to bring about violent or pronounced agitation of the molten copper.

The natural gas reformer comprises a preheated air inlet pipe 10, a natural gas inlet pipe 11, both leading into a carburetor 12 from which the carbureted mixture of gas and air at desired pressure is introduced directly into an insulated reaction chamber 13 into contact with a catalyst made of small balls 15 of nickelized alumina. A reformed gas outlet pipe 16 is connected with the reaction zone 14 of the reaction chamber 13. The outlet pipe leads into a reformed-gas cooler which, as shown, comprises a water jacket 17 surrounding the outlet pipe 16a. The water jacket has a water inlet 21 and a water outlet 22. The outlet pipe 16b is connected to a reformed-gas receiver or reservoir 18, which has a water draw-off pipe 19 equipped with a valve 20.

A reformed-gas delivery pipe 23, connected to the receiver 18 delivers reformed gas. This pipe is provided with a valve 26. A vent line 27, having a valve 28, is connected to pipe 23. Leading from control valve 26 is a pipe 30, the outer end of which is connected to a swivel connector and elbow 31, located at the end of the cylindrical furnace 32 at its axis 33. Between valve 26 and elbow 31 is connected pipe 25 leading downwardly to drip tank 24 equipped with water drawoff pipe and valve 29. A radially extending nipple 34 is connected at its inner end to swivel connector 31 and at its outer end to an elbow, in turn connected to a header pipe 35 extending along the cylindrical outside surface of the furnace 32 in an axial direction. This swivel connector arrangement 31 permits the cylindrical furnace 32 to be rotated about its axis 33 without interfering with the flow of reformed-gas into the header or bustle pipe 35. Each of two pipes 36 connected to header 35 and curved around the cylindrical surface of the furnace connects with a tuyere pipe 37. The number of pipes 36 and tuyere pipes 37 used to connect to header 35 is dependent on the flowrate of reducing gas required to accomplish the required oxygen removal within a predetermined. K

chamber lining 15a. that other suitable catalysts might be used and any suitlength of time. As shown, two tuyeres are positioned at a distance from the ends of the furnace about one: fourth the length of the furnace. With additional tuyeres, spacing is adjusted so that each tuyere influences equal volumes of charge within the anode vessel.

A typical tuyere is shown in FIG. 4, and comprises a union 40 connecting pipe 36 to a T 41 into which is threaded a tuyere pipe 42 extending through an apertured steel plate 44 secured to the steel shell 43 of the furnace in any suitable manner, as by screw bolts 48. It is significant to note that the tuyere pipe 42 extends through the magnesite brick lining 47 of the furnace and is positioned at an angle of about 15 from the level 55a of the molten copper 55 in the furnace when the furnace is in normal position, as shown in the drawings. The outlet of the tuyere is below the surface of the molten copper a sufiicient distance, and the tuyere pipe inclined at an angle so that when gas is passed through'the tuyere it creates, in effect, a stirring motion to the molten copper being treated in the furnace. If the outlet of the tuyere is about eight to twelve inches below the surface of the molten copper, this operates satisfactorily.

The furnace itself, as shown, is of conventional design, but for the gas lines and tuyeres. It had been previously used for poling copper in the conventional way. It comprises a cylindrical steel shell having a cylindrical wall43 and the end walls 45, 46, respectively; the cylindrical steel shell being lined with magnesite brick lining 47 in conventional fashion. The cylindrical wall, as shown, has an opening 50 through which poles may be inserted for a poling operation or for removal of slag and samples and through which lances, connected to a source of air under pressure, may be inserted for airblowing the molten copper, if this air-blowing is necessary, or desirable, before introducing the gaseous redu-ctant. The front end wall has an opening 51 through which the furnace is charged with molten copper. This opening may also be used for insertion of lances, if desired. A pouring spout 52 is provided opposite the opening 50 and the furnace also has an outlet 53 to a flue or stack (not shown) to carry gases from the furnace. Preferably, the furnace is insulated on its outside surface.

The furnace is mounted on rollers 54 mounted on shafts and it is equipped with conventional motordriven gearing (not shown in the drawings) so that the furnace may be rotated about its axis 33, as desired; for example, to normal position for treating the molten copper as shown in the drawings, or for rotating the cylindrical furnace for pouring molten copper through spout 52.

The following description will serve as an example of the procedure which has been followed by us successfully in actual large plant scale operations after the oxidation step, viz.: the conventional air-blowing of the molten copper. Natural gas having a composition as shown by the volumetric analysis set forth above, preheated to a temperaturer of about 1000 to 1200* F., was introduced at required pressure through natural gas inlet 11 and air in a volume about three times the volume of the natural gas, and preheated to a temperature of about 600 to 1000 F., was introduced at a pressure corresponding to that of the gas, through air inlet pipe into a carburetor 12 from which the carbureted mixture of heated air and natural gas was passed into the reaction chamber 13 of the gas reformer apparatus A. The amount of air passed into the reaction chamber is less than that which will completely burn the natural gas to CO and H 0. It should be in an amount only sufiicient to oxidize the hydrocarbons in the gas to CO while at the same time producing substantial quantities of H The mixture of air and natural gas intimately contacts the catalyst 15, which, as shown in the drawings, is made of small balls of nickelized alumina packed within the It will be understood, of course,

forming the natural gas.

The reformed natural gas, in the example now being described, was passed through the reformed-gas outlet pipe .16 at a temperature of about 1500 F. although it may be a higher or lower temperature. The reformed; gas was then passed through cooler 17, which, as shown, comprises a water jacket surrounding the conduits carrying the reformed gas. Cooling water was circulated through the jacket around the gas pipes in heat exchange relationship.

The reformed-gas was cooled in the cooler 17 to about F. It may be cooled even lower, if desired, or it may be cooled less, if it is desired to take advantage of the sensible heat in the gas in the subsequent reaction in the molten copper. The reformed-gas was then passed into gas receiver 18. The gas in the receiver may be maintained at such pressure as is found convenient. The pressure on the air and natural gas introduced through the carburetor 12 is regulated to maintain the desired pressure in the receiver. Any water in the reformed-gas which condenses and collects in the receiver is drawn off from time to time through draw-off line 19 and valve 20.

The reformed-gas, when produced as described above, showed a volumetric analysis as follows:

The reformed-gas is passed through the delivery pipe 23 and valve 26, through header 35, then through pipes 36 through tuyeres 37 beneath the surface of the molten copper 55 which has been charged into the furnace 32. In the example being described, the molten copper charge 55 had been produced by air blowing copper matte in a conventional copper converter and had then been oxidized for the production and removal of a scavenging oxide slag in the anode furnace in the conventional manner by the use of a compressed air blow-pipe inserted through opening 50 and injected into the molten bath. In this oxidation step the copper attained an oxygen content of 0.82% and a temperature of 2210 F. The rate of flow of the reformed gas through the tuyeres 37 is regulated by valve 26; the vent valve 28 being closed during the deoxidizing treatment of the copper in the furnace. The vent valve 28 is used to purge the delivery lines when first starting up the gas reformer, prior to copper treatment in the furnace.

A charge of approximately ninety-eight tons of molten copper was introduced into the treating furnace, then air-blown through lances and skimmed. After purging the delivery lines of the reformed-gas conduit system C through vent pipe 27, the reformed-gas was then passed through the valve 26 and thence through the tuyeres 37 at a rate of about 330-335 cubic feet per minute (calculated to standard conditions: 60 F. and 14.7 p.s.i.). The reformed-gas pressure should be sufiicient to overcome the hydrostatic head of molten copper above the outlet of the tuyeres and to produce sufficient gas flow velocity to bring about a stirring action of the molten copper in the furnace. p.s.i.g., have been found to be adequate. If found necessary a gas compressor or pump may be used to force the reformed-gas through the tuyeres 37. p

The following Table I shows laboratory analysis of sample test buttons taken from the molten copperbath Pressures within the range 15-30 v the ambient air.

-hours in a furnace equipped with sulficient tuyeres.

'7 55 and also the temperature of the molten charge as the treatment proceeded:

It will be seen that the oxygen content of the copper (herein called the finished product) at the end of the treatment had been reduced to below 0.10%; the oxygen in the copper having reacted with the CO and H in the reformed-gas to form CO and H which passes out of the furnace with other residual gases. This finished deoxidized molten copper was then cast in conventional molds to form copper anodes. The temperature of the molten copper at the time of casting was 2llO F., which in this instance was found to the optimal temperature for the casting operation.

Chemical analysis of the finished product which was cast into anodes (samples taken at pouring spoon) is as follows:

Table II Cu percent- 99.72 Ag oz. per ton 14.08 An do 0.595 O percent 0.17

The higher content of oxygen shown in this analysis is accounted for by the fact that the sample buttons referred to in Table I were taken from the molten copper in the furnace, whereas the sample for the analysis in Table II was taken from the stream pouring from the spoon where the molten copper had been exposed twice to the atmosphere and had taken up some oxygen from This reoxidation may be avoided, if desired, by protecting the molten copper from contact with the ambient atmospheric air.

Ninety-eight tons of anodes were cast. These anodes were equal to and were considered by some qualified 0p- .erators to be better than copper anodes previously pro duced in the same apparatus by the well-known and widely practiced poling process. The oxygen-reduced molten copper resulting from the treatment had the desirable characteristics for casting. And the finally solidified cast anodes were not only satisfactory with respect to low oxygen content but also they had the desirable density, flatness and smooth surface characteristics which are considered to be needed for eflicient operations in further refining in electrolytic cells.

The run on the 98 ton charge described above covered a period of about five and one-half hours, this time being well suited to the work schedules for eight-hour shifts. The time of treatment may be reduced if desired. A run on a 100 ton charge may be completed in 2% to 3 /2 In any event, our process lends itself admirably to work schedules where the operators work in eight-hour shifts. The amount of reformed-gas used in the illustrative run described above was 19,980 cubic feet per hour (corrected to standard conditions: 60 F. and 14.7 pounds per sq. in.).

While we have described above one particular run for purposes of illustration, it is typical of other runs that have been carried on day after day in the operation of a large smelter plant.

It will be understood also that the foregoing is merely illustrative, and certain details may vary without impairing the successful operation of our process. The amount of CO and of H in reformedgas will vary considerably in accordance with the hydrocarbon which is the source material for making the reformed gas. We have also found that hydrogen is a much more potent reductant than is carbon monoxide. It is therefore preferred when greater speed of the process is desirable and when it is desirable to use a minimum number of tuyeres. When reforming a hydrocarbon by partial oxidation with air as above described the most potent reformed gas can be made from methane (CH as compared with the other hydrocarbons in the series. For example, perfect reforming by partial oxidation with air will yield from pure methane 20.5% C0 and 41.0% H but from pentane will yield 24.5% C0 and 29.4% H Ethane, propane, butane yield intermediate values. Hydrocarbons still higher in the series will produce reformed gases having various H and CO contents. The H may be even as low as 12% and may in some instances be higher than And the CO in some instances may be as low as 12% or higher than 30%, the balance usually being substantially all nitrogen with minor amounts of incidental gases such as B 0, C0 and CH Also, it is conceivable that those wishing to practice our process might have available a spent gas or partially spent gas from some other reduction process. For example, a partially spent reformed gas from a process of reducing iron oxide to iron may contain 12% CO and 24% H Such gases have suflicient reducing power to be used in our process, but the skilled operator will have to adjust the rate at which he introduces such gas in order to not unduly lengthen the duration of time necessary to complete the reduction part of the total refining cycle. Those reformed gases having substantially less reducing power may be used in our process providing that the rate of introduction and temperature thereof are sufliciently adjusted to accomplish the result within the desired period of time to meet the operators particular total refining schedule. In the usual case, it will be important and economical that the combined CO and H in the reformed gas be present in sufficient amount, preferably 35% to and that the sensible heat in the reformed gas plus the exothermic heat of the reaction in the molten copper bath balances the heat losses from the bath. Not only does this exothermic reaction bring about the desired reduction of oxygen from the molten copper charge in the furnace, but it also aids in preventing the copper from cooling to the point where it would interfere with the subsequent casting operation.

It is significant that natural gas is usually cheap as a source material for making reformed gas. it is also significant that natural gas is already free from sulphur or can be purified at low expense with respect to sulphur. It is also significant that natural gas is predominantly methane which, as pointed out above, produces the reformed gas with the highest reducing power.

It is important in our process of accomplishing the reduction step in copper refining to prevent, insofar as possible, the entry of air from the ambient atmosphere into the furnace. If the residual gas from reaction of the reducing gases and molten copper plus any unreacted gas which rises to the surface of the molten copper is not sufiicient to prevent air from leaking into the space above the molten copper, it is desirable to further dampen or throttle the furnace gas outlet and, if necessary, to introduce additional non-oxidizing gas into this space. It may be found very advantageous to introduce natural gas into the space above the molten copper during the time that the reformed-gas is being introduced through the tuyeres. Natural gas may be introduced at a sufiicient rate to mask by yellow color the exit flame from the furnace which has otherwise the bluish-green color characteristic of a copper flame. Such natural gas addition together with the residual reformed-gases rising .to the surface of the molten copper, causes a positive gas pressure or gaseous blanket in the furnace in the space above the surface of the molten copper sufiicient to prevent atmospheric air from entering the furnace or at least takes up unwanted oxygen that may be in that space to prevent unwanted reoxidation of the molten copper by ambient atmospheric oxygen.

For illustrative purposes we have described above our process as applied to the removal of unwanted oxygen from and the refining of physical properties of copper, produced by the oxidation step in the refining of molten copper made by the air-blowing of matte inv a copper converter, for the purpose of producing in a fire-refining furnace anodes to be later refined in electrolytic cells. But it will be understood that our process is similarly applicable when wire-bars, billets, cakes, and ingots are to be produced from the fire-refining furnace instead of anodes. It will also be understood that our process is adapted to the removal of unwanted oxygen and the refining of the physical properties of molten copper made in a fire-refining furnace by melting of copper cathodes for the production of wire-bars, billets, cakes and ingots. Those skilled in the art of fire-refining of copper will understand that when our process is applied in the production of wire-bars, billets, cakes and ingots the oxygen will be reduced to a lower amount than in the production of anodes, such as 0.03 to 0.04%.

Although we have chosen to describe and illustrate the use of tuyeres for the injection of the reductant it will be understood that such injection may also be accomplished by the use of a blowpipe, by either submerging the end of the blowpipe under the surface of the molten copper or by using it non-submerged, in which case the reductant would be supplied under greater pressure so as to emerge from the end of the blowpipe at a velocity sufiicient to penetrate the molten bath to the desirable depth.

The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but

it is recognized that various modifications are possible 1 2. A process as defined in claim 1 in which the reducing gas contains suflicient CO and H to produce a sufiiciently exothermic reduction of the oxygen to maintain the copper in a molten state during the reduction process.

3. A process as defined in claim 1 in which the partial oxidation of the hydrocarbon is performed in the presence of a catalyst for this oxidation.

4. A process as defined in claim 1 in which the reducing gas produced outside of the furnace contains 12% to 50% H 12% to 30% CO and the remainder substantially all nitrogen.

5. A process as defined in claim 1 in which the hydrocarbon is natural gas.

6. A process as defined in claim 1 in which the furtrace is substantially closed and a superatmospheric pressure of non-oxidizing gas is maintained in the furnace above the surface of the molten copper during the process.

7. A process as defined in claim 3 in which the partial oxidation of the hydrocarbon is per-formed in the presence of a catalyst for this oxidation.

8. A process for converting molten copper which is ready for poling to tough-pitch copper which comprises agitating a bath of said molten copper in a furnace and reducing its oxygen content by injecting therein a reducing gas produced outside of the furnace by the partial oxidation of a hydrocarbon with an amount of air which is only sufiicient to oxidize the major part of the carbon of the hydrocarbon to CO while producing substantial quantities of free hydrogen, and continuing the injection of this gas into the molten copper until the copper is reduced to the tough-pitch stage.

9. A process as defined in claim 8 in which the reducing gas contains sufficient CO and H to produce a sufficiently exothermic reduction of the oxygen to maintain the copper in a molten state during the reduction process.

10. A process as defined in claim 8 in which the reducing gas produced outside of the furnace contains 12% to 50% H 112% to 30% CO and the remainder substantially all nitrogen.

11. A process as defined in claim 8 in which the hydrocarbon is natunal gas.

References Cited in the file of this patent UNITED STATES PATENTS 1,948,316 Scott Feb. 20, 1934 2,065,207 Betterton Dec. 22, 1936 2,741,557 Wolf Apr. 10, 1956 OTHER REFERENCES Remy: Treatise on Inorganic Chemistry, volume 1, Elsevier Publishing Co., New York 1956, pages 430432. 

1. A PROCESS OF TREATING OXYGEN-BEARING MOLTEN COPPER IN A FURNACE WHICH COMPRISES AGITATING THE MOLTEN COPPER AND REDUCING ITS OXYGEN CONTENT BY INJECTING THEREIN A REDUCING GAS PRODUCED OUTSIDE OF THE FURNACE BY THE PARTIAL OXIDATION OF A HYDROCARBON WITH AN AMOUNT OF AIR WHICH IS ONLY SUFFICIENT TO OXIDIZE THE MAJOR PART OF THE CARBON OF THE HYDROCARBON TO CO WHILE PRODUCING SUBSTANTIAL QUANTITIES OF FREE HYDROGEN. 